Overclocking the Core i7-3820
As I mentioned on the first page of this review, overclocking on the Core i7-3820 is a bit different than with any other Sandy Bridge processor out there. Because it is not fully unlocked, the multiplier is limited to 43x, about the same as the non-unlocked Core i7-2600. Unlike the original Sandy Bridge though, Sandy Bridge-E allows us to use "straps" or bus speed multipliers that still operate with the 3820.
If you remember overclocking via the base clock on SNB, going above 105-107 MHz tended to be pretty difficult. Intel addressed this on SNB-E by offering "straps" that basically act as multipliers on the base clock. So on most motherboards you will see the option for a strap of 125 MHz or 1.25x, depending on the vendor, and that is how we were able to get past the multiplier limit of 43x to see higher overall speeds.
On Intel’s DX79SI motherboard, they call it the "1.25x Profiles" that puts the processor base clock at 125 MHz and sets the voltages accordingly. Intel’s motherboard engineers actually did a very good job making this process easy as it only took a couple of BIOS changes to make it happen.
These are the result voltage and limit changes set by simply enabling the 1.25x profile on the DX79SI motherboard – again a very positive overclocking experience! When you set this mode though there aren’t many options that Intel allows you to change – what you see if what you get.
The base clock speed brought us to a 4.5 GHz clock rate…
Though I found that moving to a 37x multiplier was the highest I was able to go without being able to adjust the voltage any higher. This clock speed worked even with all the cores enabled, so we are essentially seeing a 700 MHz boost over the default settings of the Core i7-3820!
In our CineBench tests, the default scores were 6,134 and 24,352 respectively and we see the above results are 24% and 22% faster.
Our previous POV-Ray result was a score of 5,267, giving the overclocked Core i7-3820 a more than 23% performance boost.
While overclocking on the "partially unlocked" processor was a bit more complicated, hitting 4.63 GHz on the CPU is pretty impressive and takes the $285 processor much closer to the performance of the 6-core Sandy Bridge-E variants at their default settings, at least in those highly threaded cases. For fewer threads, these high clock speeds would be able to beat out the default configurations of basically any CPU on the market. Not bad for under a 3-spot.
Keep in mind that this overclocking definitely raises the power consumption and TDP of the processor.
At the overclocked speed of 4.63 GHz the Intel Core i7-3820 uses 90 additional watts of power – that’s a 50% increase for the entire system! Make sure you have a good cooler (we used the Intel water cooler kit) to make sure things stay out of the red.